Debt - Convertible Senior Notes Due 2024 (Details) $ / shares in Units, shares in Thousands		6 Months Ended
	Jul. 05, 2017 USD ($) $ / shares	Mar. 31, 2024 USD ($) $ / shares shares	Sep. 30, 2023 USD ($)	Mar. 31, 2023 USD ($)
Debt Instrument [Line Items]
Amount outstanding		$ 367,762,000	$ 367,762,000	$ 367,762,000
Senior Notes
Debt Instrument [Line Items]
Amount outstanding		367,762,000
2024 Convertible Notes | Common Class A
Debt Instrument [Line Items]
Conversion rate per $1,000 principal amount	0.1
If-converted value in excess of principal amount		$ 2,200,000
Number of shares potentially issuable | shares		205
2024 Convertible Notes | Senior Notes
Debt Instrument [Line Items]
Stated interest rate	2.875%
Principle amount	$ 143,750,000
Amount outstanding		$ 34,389,000
Effective interest rate		3.35%
Conversion price, per share (in dollars per share) | $ / shares	$ 10.00	$ 10.00